Characterization of Avian-like Influenza A (H4N6) Virus Isolated from Caspian Seal in 2012

Pinnipeds and avian influenza: a global timeline and review of research on the impact of highly pathogenic avian influenza on pinniped populations with particular reference to the endangered Caspian seal (Pusa caspica)

This study reviews chronologically the international scientific and health management literature and resources relating to impacts of highly pathogenic avian influenza (HPAI) viruses on pinnipeds in order to reinforce strategies for the conservation of the endangered Caspian seal (Pusa caspica), currently under threat from the HPAI H5N1 subtype transmitted from infected avifauna which share its haul-out habitats. Many cases of mass pinniped deaths globally have occurred from HPAI spill-overs, and are attributed to infected sympatric aquatic avifauna. As the seasonal migrations of Caspian seals provide occasions for contact with viruses from infected migratory aquatic birds in many locations around the Caspian Sea, this poses a great challenge to seal conservation. These are thus critical locations for the surveillance of highly pathogenic influenza A viruses, whose future reassortments may present a pandemic threat to humans.

Highly pathogenic avian influenza H5N1 virus infections in pinnipeds and seabirds in Uruguay: Implications for bird-mammal transmission in South America

The highly pathogenic avian influenza viruses of clade 2.3.4.4b have caused unprecedented deaths in South American wild birds, poultry, and marine mammals. In September 2023, pinnipeds and seabirds appeared dead on the Uruguayan Atlantic coast. Sixteen influenza virus strains were characterized by real-time reverse transcription PCR and genome sequencing in samples from sea lions (Otaria flavescens), fur seals (Arctocephalus australis), and terns (Sterna hirundinacea). Phylogenetic and ancestral reconstruction analysis showed that these strains have pinnipeds most likely as the ancestral host, representing a recent introduction of clade 2.3.4.4b in Uruguay. The Uruguayan and closely related strains from Peru (sea lions) and Chile (sea lions and a human case) carry mammalian adaptative residues 591K and 701N in the viral polymerase basic protein 2 (PB2). Our findings suggest that clade 2.3.4.4b strains in South America may have spread from mammals to mammals and seabirds, revealing a new transmission route.

Cross-Species Transmission Potential of H4 Avian Influenza Viruses in China: Epidemiological and Evolutionary Study

H4 avian influenza viruses (AIVs) have been widely detected in live poultry markets in China. However, the potential public health impact of H4 AIVs remains largely uncertain. Here, we fully analyzed the distribution and phylogenetic relationship of H4 AIVs in China. We obtained 31 isolates of H4 viruses in China during 2009-2022 through surveillance in poultry-associated environments, such as live poultry markets and poultry farms. Genomic sequence analysis together with publicly available data revealed that frequent reassortment and introduction of H4 AIV from wild birds to poultry may have occurred. We identified 62 genotypes among 127 whole genome sequences of H4 viruses in China, indicating that H4 AIVs had great genetic diversity in China. We also investigated molecular markers and found that drug resistance mutations frequently occurred in the M2 protein and a few mutations related to receptor binding and the host signature in H4 AIVs. Our study demonstrates the cross-species transmission potential of H4 AIVs in China and provides some reference significance for its risk assessment.

Genetic and Biological Characteristics of Duck-Origin H4N6 Avian Influenza Virus Isolated in China in 2022

The interaction between migratory birds and domestic waterfowl facilitates viral co-infections, leading to viral reassortment and the emergence of novel viruses. In 2022, samples were collected from duck farms around Poyang Lake in Jiangxi Province, China, which is located within the East Asia-Australasia flyway. Three strains of H4N6 avian influenza virus (AIV) were isolated. Genetic and phylogenetic analyses showed that the isolated H4N6 avian influenza viruses (AIVs) belonged to new genotypes, G23 and G24. All isolated strains demonstrated dual receptor binding properties. Additionally, the isolated strains were able to replicate efficiently not only in avian cells but also in mammalian cells. Furthermore, the H4N6 AIV isolates could infect chickens, with viral replication detected in the lungs and extrapulmonary organs, and could transmit within chicken flocks through contact, with viral shedding detected only in oropharyngeal swabs from chickens in the contact group. Notably, the H4N6 AIV could infect mice without prior adaptation and replicate in the lungs with high viral titers, suggesting that it is a potential threat to humans. In conclusion, this study provides valuable insight into the characteristics of H4N6 strains currently circulating in China.

Mass mortality event in South American sea lions (Otaria flavescens) correlated to highly pathogenic avian influenza (HPAI) H5N1 outbreak in Chile

In Chile, since January 2023, a sudden and pronounced increase in strandings and mortality has been observed among South American (SA) sea lions (Otaria flavescens), prompting significant concern. Simultaneously, an outbreak of highly pathogenic avian influenza H5N1 (HPAIV H5N1) in avian species has emerged since December 2022. To investigate the cause of this unexpected mortality, we conducted a comprehensive epidemiological and pathologic study. One hundred sixty-nine SA sea lions were sampled to ascertain their HPAIV H5N1 status, and long-term stranding trends from 2009 to 2023 were analyzed. In addition, two animals were necropsied. Remarkably, a significant surge in SA sea lion strandings was observed initiating in January 2023 and peaking in June 2023, with a count of 4,545 stranded and deceased animals. Notably, this surge in mortality correlates geographically with HPAIV outbreaks affecting wild birds. Among 168 sampled SA sea lions, 34 (20%) tested positive for Influenza A virus, and 21 confirmed for HPAIV H5N1 2.3.4.4b clade in tracheal/rectal swab pools. Clinical and pathological evaluations of the two necropsied stranded sea lions revealed prevalent neurological and respiratory signs, including disorientation, tremors, ataxia, and paralysis, as well as acute dyspnea, tachypnea, profuse nasal secretion, and abdominal breathing. The lesions identified in necropsied animals aligned with observed clinical signs. Detection of the virus via immunohistochemistry (IHC) and real-time PCR in the brain and lungs affirmed the findings. The findings provide evidence between the mass mortality occurrences in SA sea lions and HPAIV, strongly indicating a causal relationship. Further studies are needed to better understand the pathogenesis and transmission.

Zoonotic Animal Influenza Virus and Potential Mixing Vessel Hosts

Influenza viruses belong to the family Orthomyxoviridae with a negative-sense, single-stranded segmented RNA genome. They infect a wide range of animals, including humans. From 1918 to 2009, there were four influenza pandemics, which caused millions of casualties. Frequent spillover of animal influenza viruses to humans with or without intermediate hosts poses a serious zoonotic and pandemic threat. The current SARS-CoV-2 pandemic overshadowed the high risk raised by animal influenza viruses, but highlighted the role of wildlife as a reservoir for pandemic viruses. In this review, we summarize the occurrence of animal influenza virus in humans and describe potential mixing vessel or intermediate hosts for zoonotic influenza viruses. While several animal influenza viruses possess a high zoonotic risk (e.g., avian and swine influenza viruses), others are of low to negligible zoonotic potential (e.g., equine, canine, bat and bovine influenza viruses). Transmission can occur directly from animals, particularly poultry and swine, to humans or through reassortant viruses in "mixing vessel" hosts. To date, there are less than 3000 confirmed human infections with avian-origin viruses and less than 7000 subclinical infections documented. Likewise, only a few hundreds of confirmed human cases caused by swine influenza viruses have been reported. Pigs are the historic mixing vessel host for the generation of zoonotic influenza viruses due to the expression of both avian-type and human-type receptors. Nevertheless, there are a number of hosts which carry both types of receptors and can act as a potential mixing vessel host. High vigilance is warranted to prevent the next pandemic caused by animal influenza viruses.

An early warning system for highly pathogenic viruses borne by waterbird species and related dynamics of climate change in the Caspian Sea region: Outlines of a concept

Aim. Formulation of the outlines of the concept of ViEW (Viral Early Warning) which is intended as a long term system of multidisciplinary transboundary cooperation between specialist institutions of all five Caspian region states to research, regularly monitor and share data about the generation, transmission and epidemiology of avian‐borne pathogens and their vectors in the region, and the ways climate change may affect these processes.

Material and Methods. The concept is based on the multidisciplinary experience of the authors in researching the processes incorporated in the ViEW concept and on an in‐depth survey of the literature involved.

Results. The outlines of the ViEW concept are presented in this study for review and comment by interested parties and stakeholders.

Conclusion. Review of activities and opinions of specialists and organizations with remits relating to the development, establishment and maintenance of ViEW, indicates that such a system is a necessity for global animal and human health because of the role that the Caspian region plays in the mass migration of species of waterbird known as vectors for avian influenza and the already evident impacts of climate change on their phenologies. Waterbirds frequenting the Caspian Sea littorals and their habitats together constitute a major potential global hotspot or High Risk region for the generation and transmission of highly pathogenic avian influenza viruses and other dangerous zoonotic diseases.

ANTIBODIES AGAINST INFLUENZA VIRUS TYPES A AND B IN CANADIAN SEALS

Influenza viruses have been reported from marine mammals worldwide, particularly in pinnipeds, and have caused mass mortalities of seals in North America and Europe. Because influenza viruses in marine mammals can be zoonotic, our objective was to examine Canadian phocids for exposure to influenza A and B viruses in order to understand health risks to wild populations as well as to humans who consume or handle these animals. Blood was collected from 394 seals in eastern Canada from 1994 to 2005. Sera were screened for exposure to influenza viruses in three resident species of seals: harbour, Phoca vitulina (n=66); grey, Halichoerus grypus (n=82); ringed, Phoca hispida (n=2); and two migrant species: harp, Pagophilus groenlandica (n=206) and hooded, Cystophora cristata (n=38). Included were samples from captive grey (n=1) and harbour seals (n=8) at two aquaria. Sera were prescreened using indirect enzyme-linked immunosorbent assay (ELISA), and antibodies against influenza A virus were confirmed using a commercial competitive ELISA (IDEXX Europe B.V.). A subset of influenza A virus positive sera was used to determine common virus subtypes recognized by sera using reference strains. All positive sera in the indirect ELISA reacted with influenza A virus subtypes H3, H4, and H10 using a hemagglutination inhibition assay. Sera from harbour, grey, harp, and hooded seals had antibodies against influenza A and influenza B viruses (some cross-reactivity occurred). Overall, 33% (128/385) of wild seals were seropositive to influenza viruses, with the highest seroprevalence in harp (42%) followed by harbour (33%), grey (23%), and hooded (11%) seals. Antibodies were detected in both sexes and most age classes of wild seals. Two of eight captive harbour seals were seropositive to influenza B virus and four had cross-reactions to influenza A and B viruses. This study reports antibodies against influenza A and B viruses in four seal species from the same geographic area in eastern Canada.

Hemagglutinin Stability and Its Impact on Influenza A Virus Infectivity, Pathogenicity, and Transmissibility in Avians, Mice, Swine, Seals, Ferrets, and Humans

Genetically diverse influenza A viruses (IAVs) circulate in wild aquatic birds. From this reservoir, IAVs sporadically cause outbreaks, epidemics, and pandemics in wild and domestic avians, wild land and sea mammals, horses, canines, felines, swine, humans, and other species. One molecular trait shown to modulate IAV host range is the stability of the hemagglutinin (HA) surface glycoprotein. The HA protein is the major antigen and during virus entry, this trimeric envelope glycoprotein binds sialic acid-containing receptors before being triggered by endosomal low pH to undergo irreversible structural changes that cause membrane fusion. The HA proteins from different IAV isolates can vary in the pH at which HA protein structural changes are triggered, the protein causes membrane fusion, or outside the cell the virion becomes inactivated. HA activation pH values generally range from pH 4.8 to 6.2. Human-adapted HA proteins tend to have relatively stable HA proteins activated at pH 5.5 or below. Here, studies are reviewed that report HA stability values and investigate the biological impact of variations in HA stability on replication, pathogenicity, and transmissibility in experimental animal models. Overall, a stabilized HA protein appears to be necessary for human pandemic potential and should be considered when assessing human pandemic risk.

Biological Properties and Genetic Characterization of Novel Low Pathogenic H7N3 Avian Influenza Viruses Isolated from Mallard Ducks in the Caspian Region, Dagestan, Russia

Avian influenza viruses (AIVs) are maintained in wild bird reservoirs, particularly in mallard ducks and other waterfowl. Novel evolutionary lineages of AIV that arise through genetic drift or reassortment can spread with wild bird migrations to new regions, infect a wide variety of resident bird species, and spillover to domestic poultry. The vast continental reservoir of AIVs in Eurasia harbors a wide diversity of influenza subtypes, including both highly pathogenic (HP) and low pathogenic (LP) H7 AIV. The Caspian Sea region is positioned at the intersection of major migratory flyways connecting Central Asia, Europe, the Black and Mediterranean Sea regions and Africa and holds a rich wetland and avian ecology. To understand genetic reservoirs present in the Caspian Sea region, we collected 559 cloacal swabs from Anseriformes and other species during the annual autumn migration periods in 2017 and 2018. We isolated two novel H7N3 LPAIV from mallard ducks whose H7 hemagglutinin (HA) gene was phylogenetically related to contemporaneous strains from distant Mongolia, and more closely Georgia and Ukraine, and predated the spread of this H7 LPAIV sublineage into East Asia in 2019. The N3 neuraminidase gene and internal genes were prototypical of AIV widely dispersed in wild bird reservoirs sampled along flyways connected to the Caspian region. The polymerase and nucleoprotein segments clustered with contemporaneous H5 HPAI (clade 2.3.4.4b) isolates, suggesting the wide dispersal of H7 LPAIV and the potential of this subtype for reassortment. These findings highlight the need for deeper surveillance of AIV in wild birds to better understand the extent of infection spread and evolution along spatial and temporal flyways in Eurasia.

A Brief Introduction to Influenza A Virus in Marine Mammals

Influenza A infection has been detected in marine mammals going back to 1975, with additional unconfirmed outbreaks as far back as 1931. Over the past forty years, infectious virus has been recovered on ten separate occasions from both pinnipeds (harbor seal, elephant seal, and Caspian seal) and cetaceans (striped whale and pilot whale). Recovered viruses have spanned a range of subtypes (H1, H3, H4, H7, H10, and H13) and, in all but H1N1, show strong evidence for deriving directly from avian sources. To date, there have been five unusual mortality events directly attributed to influenza A virus; these have primarily occurred in harbor seals in the Northeastern United States, with the most recent occurring in harbor seals in the North Sea.There are numerous additional reports wherein influenza A virus has indirectly been identified in marine mammals; these include serosurveillance efforts that have detected influenza A- and B-specific antibodies in marine mammals spanning the globe and the detection of viral RNA in both active and opportunistic surveillance in the Northwest Atlantic. For viral detection and recovery, nasal, rectal, and conjunctival swabs have been employed in pinnipeds, while blowhole, nasal, and rectal swabs have been employed in cetaceans. In the case of deceased animals, virus has also been detected in tissue. Surveillance has historically been somewhat limited, relying largely upon opportunistic sampling of stranded or bycaught animals and primarily occurring in response to a mortality event. A handful of active surveillance projects have shown that influenza may be more endemic in marine mammals than previously appreciated, though live virus is difficult to recover. Surveillance efforts are hindered by permitting and logistical challenges, the absence of reagents and methodology optimized for nonavian wild hosts, and low concentration of virus recovered from asymptomatic animals. Despite these challenges, a growing body of evidence suggests that marine mammals are an important wild reservoir of influenza and may contribute to mammalian adaptation of avian variants.